Using the bridging mode in Amplifier

[Dave5000]

I need to take one output for tops and use 2xAmps to run them. There is obviously the usual output from the desk and without the experience I am asuming you put the left output into one amp and the right output into the other amp?

 

is it as simple as this or does anyone have a more efficient and better way?

 

this will all be running through a graphic and crossover first if that makes a difference?

[Mr.Si]

This sounds similar to a situation I have had in the past, where 4 all my speakers were 4 Ohm, but I needed to drive two per side. My amp though, would only drive a minimum load of four ohms, thus making it not possible for me to parallel 2 speakers on each amp channel. So I had to use one amp per side.

 

Getting on to answer your question, I am going by what I was told by other pro's/hire companies etc. (not on here).

 

Don't use the bridging mode because the amp will distort much more.

Instead, use a splitter cable on the input of each amp (thus keeping it in stearo mode) and connect all speakers with separate leads.

 

So, trying not to complicate things further!...

 

1. Conncect the left channel from your desk to both channels on Amp 1 by using a Y splitter lead.

 

2. Connect the right channel from your desk to both channels on Amp 2 by using a Y splitter lead.

 

3. Connect the left speakers individually to both outputs of Amp 1

 

4. Connect the right speakers individually to both outputs of Amp 2

 

This does though, mean you'd probably have to use more long speaker leads.

 

Hope this makes sense.

 

Simon

[paulears]

DON'T connect both outputs from an amp together! Mr Si's got me a little confused here - but seems to be saying combine the inputs and combine the outputs and use two amps - one for left, one for right.

 

 

Dave - do you mean you have a mono desk output and want to run left from one amp bridging to get extra power and right from another amp also set to bridge?

 

If you have amps capable of providing bridging to one output, then input switching is usually provided so that you only need one input, and just one knob for level.

 

If this is correct - then there shouldn't be a problem. Loads of people do it this way when they have a single cabinet that can handle more than the separate outputs from the amp. Quality is not an issue on decently designed kit.

 

Mr Si's method of paralleling outputs seems a very expensive way to find out if your amp has decent protection. Bridge mode does not parallel outputs, it just adds the output of one channel to the other. I don't quite get the speaker lead thing - unless he's talking about using two cables to the loudspeaker and using the two sockets as the combiner - please say this isn't the case!

 

As for the problem with 2 x 4 ohm speakers and a minimum 4 ohm amp. Canford have some neat little plastic boxes with 3 speakons. You just wire it internally as a series split, and your two speakers work fine with everyone happy! If no plastic box, then a short y splitter can be wired as a series split quite simply.

 

paul

[Dave5000]

Cheers guys.

 

I think I just need to get my head round this.

 

just got off the phone and was told this: -

 

I am trying to run 6x full range tops and 6x 18 Bins, the problem being I have tree amps to do this. (not me, the client).

 

coming out of the crossover I will send a signal to the left channel of amp A (stereo Mode) and link to Left channel of Amp B (Parallel Mode). This means that Amp A`s Left channel will power the first 2 Tops and Amp B will power the other 4 tops using left and right output channels!

 

Nightmare!

 

The low frquency will run into the right channel of Amp A (Stereo Mode) and link out to Amp C (Parallel Mode) thus powering the bins between them.

 

How does this sound?

[bruce]

I don't think Si is suggesting connecting outputs together at all.... although there aree a few things I'm not clear about in his posting. Does he really mean long speaker leads or long signal leads?

 

I think he's suggesting using 4 speakers and 2xstereo amps, one for left and one for right.....

 

Bruce.

[paulears]

A lkot depends on the amps you have, but with 6 subs and 6 tops, I'd run 3 tops from ch 1, amp 1 - 3 tops ch2, amp 1 direct from the hf output of the x-over. The other two lf outs from the x-over I'd send to amp 2 ch 1 and 2 - with a link to amp3 ch 1 and 2. You may be lucky and find the amps already have link outs just for this purpose.

 

You end up with 3 amps all having l&r controls that do the same thing - i.e. left and right

 

 

AMP 1-1 HF out from x-over left channel - to 3 tops

AMP 1-2 HF out from x-over right channel - to 3 tops

AMP 2-1 LF out from x-over left channel - to 2 subs

AMP 2-2 LF out from x-over right channel - to 2 subs

AMP 3-1 LF out from x-over left channel - to 1 subs

AMP 3-2 LF out from x-over right channel - to 1 subs

 

Only thing will be to set the relative balance of the amp running 2 subs against the one running 1 to ensure you don't overdrive the single sub

 

This assumes the amp 1 is happy to run 3 spkrs in parallel - I've used this type of set up quite often and as long as the amp 1 is high enough powered to drive 3 tops all should be well.

[andy_s]

I thought bridging turned a stereo amp with two outputs into a mono amp with one output - not a mono amp with two parallel outputs. Is this correct? - on my old soundcraft amps which have binding post speaker connections, to run bridged, I would take the +ve from A and the -ve output from B to get a single speaker feed, which I could then split at the speaker end in order to run more than one box in series or parallel according to what impedance I need to see.

 

I've never actually done this, so I've no idea what I might blow up......

[paulears]

dead right andy - that's exactly what it does.

 

I think we've all got a bit confused about the question - but daves later post seems to have clarified things now.

[lonfire]

hi,

some speaker power ratings/ohm and amp powers might be useful..

 

what you suggested would probably work:

 

AMP 1 - stereo

L = 2xtops

R = 2xbins

 

AMP 2 - bridged

L = 4xtops

 

AMP 3 - bridged

R = 4xbins

 

you will find that if you pan left and right you get a different balance of top and bass though, so keep it mono..

 

what are peoples thoughts about running one side of an amp for bass and the other for top? I tend to use one amp for two subs and the other for two tops..

 

don't forget two 8 ohm speakers in parallel = 4 ohms, two 4 ohm speakers in parallel = 2 ohms.. so check your amps can operate that low, and if your speakers are 4 ohms to start with that'll drop the overall impedance to 1ohm! (for the amps running 4x speakers that is)..

 

perhaps this would be slightly better if the low impedance is a problem:

 

AMP 1 - stereo

L = 2xtops

R = 2xbins

 

AMP 2 - stereo

L = 2xtops

R = 2xtops

 

AMP 3 - stereo

L = 2xbins

R = 2xbins

 

hope this helps?

 

rgds

chris

 

ps.

if your using an active crossover it'll be more like: (using my second suggestion of using the amps in stereo)

 

Desk -> crossover (L+R)

 

Bass L = AMP 3 L

Bass R = AMP 3 R

link out from either L or R into AMP 1 R

 

Tops L = AMP 2 L

Tops R = AMP 2 R

link out from either L or R into AMP 1 L

 

that is if your amps have link out XLRs (or jacks) if not you'll need 2xY leads

[Mr.Si]

DON'T connect both outputs from an amp together! Mr Si's got me a little confused here - but seems to be saying combine the inputs and combine the outputs and use two amps - one for left, one for right.

 

 

<{POST_SNAPBACK}>

 

I wasn't saying combine the outputs, that'd be so wrong, surely.

 

Just combining the inputs and use both the outputs individually thus taking each output to a different speaker.

 

Sorry for causing confusion there. I predicted I might have! :(

 

:unsure:

[Dave5000]

if I come out of the crossover and split one signal cable into 2 will this cause a drop in signal?

 

basically 2 of the amps do not have the parallel mode option and I am a bit stuck now.

 

how efficient is this going to be having them all in stereo and sharing signals from the crossover?

[Mr.Si]

if I come out of the crossover and split one signal cable into 2 will this cause a drop in signal?

 

I've never experienced any noticeable drop in signal. So if you come out of the crossover (Which may have given it a little amplification of its own anyway), it would be doing the same think as using the link out on the more expensive amps.

 

Si

[bruce]

if I come out of the crossover and split one signal cable into 2 will this cause a drop in signal?

 

Power amps should have a high impedance input - 30K is not uncommon - so using a splitter cable should not make any noticeable difference to the levels.

 

In an ideal world, you'd use a DA, but unless I was driving long cables or needed control over individual levels, I probably wouldn't bother....

 

Bruce.

[paulears]

basically 2 of the amps do not have the parallel mode option and I am a bit stuck now.

 

how efficient is this going to be having them all in stereo and sharing signals from the crossover?

<{POST_SNAPBACK}>

 

 

I don't see what the problem is. Essentially, at it's simplest - you have a crossover with two hf outputs, and 2 lf outputs. Split these to get the extra couple of amp inputs you want. As Bruce says - there isn't a problem here.

 

So 3 stereo amps from two stereo outputs works fine. You just have to decide how many amps you dedicate to LF? One or two? It really depends on the sound you are trying to create - solid thundery sub - or if the tops are pretty full range anyway, more power to them. If you make the splitters, you can try both and see which sound you like best.